The invention relates to a lifting device for the lower steering arms of an attaching device of a tractor or self-driving implement.
Tractors, or self-driving implements, at their rear or, optionally, also at their front, include an attaching device. The attaching device has lower steering arms which are offset in the direction opposite to the longitudinal axis of the tractor or self-driving implement. One end of the lower steering arms is articulatable. It is attached at the rear and/or front to be pivotable around a substantially horizontal axis. In addition, a slight lateral pivotability exists. At their free ends, the lower steering arms includes couplings to connect with an implement. A lifting device is provided to pivot the lower steering arms. The lifting device, which carries an implement attached to the lower steering arms, raises or lowers the implement relative to the ground. Furthermore, as a function of the implement to be attached and the type of application, the lifting device must enable the lower steering arms, to a certain extent, to move freely sideways to a certain extent. In other applications, free pivotability in the vertical direction is essential. In particular, some types of lifting devices which are integrated into the tractor or the implement and include two parallel lifting arms, are connected to the ends of a lifting shaft. The lifting shaft itself is pivoted by a drive. Thus, the lifting arms move in a circular arch. Lifting struts, which are connected to the lower steering arms, are secured to the ends of the lifting arms. In addition, the lifting shaft ensures synchronization of the two lifting arms. A precision adjustment mechanism is arranged at the rear of the lifting device to improve adaptability. The adjustment mechanism adjusts the length of the lifting struts. Furthermore, an assembly is provided which optionally enables a rigid connection with the lower steering arm or disconnection and free vertical mobility. The assembly enables a vertical floating path for yawing the implement. The assembly compensates for transverse inclinations in order to enable tension-free operation.
In the case of a lifting device attached to the front of the tractor or implement, the lower steering arms are normally connected to one another to form a rocker. The drive is in the form of two hydraulic lifting struts. The struts are connected directly to the lower steering arms. An oblong hole in the coupling element is provided to compensate for vertical degrees of freedom in transverse inclinations.
Such an assembly is described in WO 96/03024. The two hydraulic lifting struts can be connected by a common hydraulic line to a pump or to a pressure supply source. This means that the pressure level is the same for both hydraulic lifting struts. Thus, they are both supplied with the same amount of pressure.
Although the above-described types of lifting devices have different designs, they have a common characteristic. The synchronous movements of the two lower steering arms is ensured and a vertical degree of freedom is available. The hydraulic lifting struts are disadvantageous because accurate uniform operation is not ensured due to leakages which can lead to different settings in spite of identical pressure levels.